Rotor blade having passive bleed path

ABSTRACT

A rotor blade includes a bleed path opening to a suction surface, extending through the blade, exiting to at least one of the suction or a trailing surface, and through which working fluid flows under centrifugal pumping forces when the blade rotates, to passively bleed working fluid from the suction surface.

BACKGROUND

1. Technical Field

This invention relates generally to rotors having radially extendingworking members and, more particularly, to impellers and propellershaving blades with fluid passages open to a working fluid.

2. Description of the Related Art Including Information Disclosed Under37 CFR 1.97 and 1.98

Rotors typically include a hub for coupling to some other device like aprime mover or an electrical machine, and one or more radially extendingworking members for acting on, or reacting with, a working fluid. Forexample, an aircraft propeller typically includes a hub coupled to anengine output shaft, and several blades extending radially outwardlyfrom the hub. The engine output shaft rotates the hub to rotate theblades, which convert rotational forces into aerial thrust forces topropel an aircraft through the air. In another example, a wind turbineimpeller typically includes a hub coupled to a generator input shaft,and several blades extending radially outwardly from the hub. Windimpacts the blades, which convert wind thrust to hub rotation forrotating the generator input shaft to generate electricity within thegenerator. Similar examples exist for marine propellers, turbine enginerotors, helicopter rotors, and the like.

BRIEF SUMMARY

A rotor blade includes a root region, a tip region disposed radiallyoutwardly of the root region, leading and trailing surfaces extendingbetween the root and tip regions, and pressure and suction surfacesextending between the root and tip regions and the leading and trailingsurfaces. The blade also includes a bleed path that opens to the suctionsurface, extends through the blade, and exits to at least one of thesuction or trailing surfaces. Working fluid flows through the bleed pathunder centrifugal pumping forces when the blade rotates, to passivelybleed working fluid from the suction surface.

Additionally provided is a rotor including the aforementioned rotorblade, wherein the bleed path is configured such that the working fluidpassively flows through the bleed path under negative pressurization,but does not actively flow therethrough by positive pressurization fromsome external pressurizing device or from a path open to the pressuresurface. The bleed path includes an inlet in the suction surface toreceive the working fluid on the suction surface, a conduit incommunication with the inlet to convey the working fluid from the inlettoward the tip region, and an outlet in communication with the conduitand disposed radially outwardly of the inlet to exhaust the workingfluid out of the blade.

Also provided is a rotor blade that includes a root region, a tip regiondisposed radially outwardly of the root region, leading and trailingsurfaces extending between the root and tip regions, and pressure andsuction surfaces extending between the root and tip regions and theleading and trailing surfaces. The rotor blade also includes a bleedpath opening to the suction surface and including an inlet in thesuction surface to receive working fluid on the suction surface. Thebleed path further includes a conduit in communication with the inlet toconvey the working fluid from the inlet toward the tip region, and anoutlet in communication with the conduit and disposed radially outwardlyof the inlet to exhaust the working fluid out of the blade.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

These and other features and advantages will become apparent to thoseskilled in the art in connection with the following detailed descriptionand drawings of one or more embodiments of the invention, in which:

FIG. 1 is a plan view of an example embodiment of a rotor including ahub and blades;

FIG. 2 is an enlarged cross-sectional view through line 2-2 of one ofthe blades of FIG. 1;

FIG. 3 is an enlarged fragmentary side view taken along line 3 of one ofthe blades of FIG. 1;

FIG. 4 is an enlarged fragmentary perspective view of one of the bladesof FIG. 1;

FIG. 5 is an enlarged cross-sectional view of a prior art rotor blade,and illustrating laminar separation of a working fluid with respectthereto; and

FIG. 6 is an enlarged cross-sectional view of an exemplary rotor bladehaving a bleed path, and illustrating attached flow of a working fluidwith respect thereto.

DETAILED DESCRIPTION

FIG. 1 illustrates an exemplary embodiment of a rotor 10 including a hub12 defining a rotational axis A of the rotor 10, which is intended torotate in a counter-clockwise direction about the axis A. The rotor 10also includes one or more of a rotor blade 14 extending generallyradially outwardly from the hub 12 along a longitudinal axis B of theblade 14. Although three separate blades 14 are shown, any suitablequantity of blades may be used. In general, the components of the rotor10 can be manufactured according to techniques known to those skilled inthe art, including casting, forging, molding, machining, stamping,and/or the like. Likewise, any suitable materials can be used in makingthe components, such as metals like aluminum or steel, composites,polymeric materials, and/or the like.

The example embodiment will be described and illustrated with referenceto its use in an aircraft propeller environment. However, it will beappreciated as the description proceeds that the invention is useful inmany different applications and may be implemented in many otherembodiments. In this regard, and as used herein and in the claims, itwill be understood that the term “rotor” refers not only to aircraftpropeller applications, but also to windmill impellers, marinepropellers, turbine engine rotors, helicopter rotors, and various otherapplications, and regardless of the type of working fluid used inconjunction with the rotor.

Still referring to FIG. 1, the blade 14 includes a root region 16proximate the hub 12, and a tip region 18 distal the hub 12 and disposedradially outwardly of the root region 16. The root region 16 may beintegrally or separately coupled to the hub 14 for example, by forming,casting, forging, welding, fastening, or in any other suitable manner.The tip region 18 may include a radially outermost surface 20 of theblade 14. The blade 14 also includes a leading edge or surface 22extending between the root and tip regions 16, 18, and a trailing edgeor surface 24 extending between the root and tip regions 16, 18. Theleading and trailing surfaces 22, 24 may be rounded, flat, pointed,and/or of any other suitable shape(s).

Referring also to FIG. 2, the blade 14 further includes a first orpressure surface 26 extending between the root and tip regions 16, 18(FIG. 1) and the leading and trailing surfaces 22, 24, and a second orsuction surface 28 extending between the root and tip regions 16, 18(FIG. 1) and the leading and trailing surfaces 22, 24. The suctionsurface 28 may be generally convex as shown and the pressure surface 26may be generally concave as shown, wherein the blade 14 may be shaped asan aerofoil. However, the suction and pressure surfaces 26, 28 may be ofany suitable shape(s) or contour(s) and the blade 14 need not beaerofoil-shaped and may be of any suitable shape and disposed at anysuitable angle(s).

With continuing reference to FIGS. 1 and 2, the blade 14 additionallyincludes a bleed path 30 opening to the suction surface 28, extendingthrough the blade 14, and exiting to the suction surface 28, thetrailing surface 24, or both. The bleed path 30 is provided to bleed lowenergy working fluid from the suction surface 28 to improve bladeefficiency. Working fluid flows into, through, and out of the bleed pathunder centrifugal pumping forces to passively bleed working fluid fromthe suction surface 28 and thereby prevent or reduce boundary layerseparation and/or a laminar separation bubble of working fluid on thesuction surface 28.

As shown in FIG. 1, the bleed path 30 generally may extend along, orparallel with respect to, the blade axis B. However, the bleed path 30may be disposed at any suitable angle with respect to the axis B, andneed not be centered between the leading and trailing surfaces 22, 24.As also shown in FIG. 1, the bleed path 30 may be disposed radiallyoutwardly of a circumferential axis C that may bisect the length of theblade 14. In another embodiment, a portion of the bleed path 30 mayextend radially inwardly of the axis C. For example, at least part of aninlet portion of the bleed path 30 may extend radially inwardly of theaxis C.

Still referring to FIG. 1, the bleed path 30 includes an inlet 32located in the suction surface 28 to receive working fluid on thesuction surface 28, and a conduit 34 in communication with the inlet 32to convey the working fluid from the inlet 32 in a radially outwarddirection toward the tip region 18 of the blade 14. As shown in FIGS. 1and 3, the bleed path 30 also includes an outlet 36 in communicationwith the conduit 34 and disposed radially outwardly of the inlet 32 toexhaust the working fluid out of the blade 14.

Referring to FIG. 4, and as depicted by the arrows, centrifugal pumpingforces pull working fluid into the inlet 32, through the conduit 34, andout of the outlet 36. (See FIG. 1 for example location of outlet 36 inthe blade 14) Such fluid flow may reduce or thin a boundary layer, andalso may at least reduce, and preferably prevent, laminar separation ofthe working fluid on the suction surface 28 of the blade 14. The workingfluid passively flows through the bleed path 30 under vacuum or negativepressurization pulled from the outlet 36. In other words, the workingfluid may not actively flow through the bleed path 30 under positivepressurization pushed from the inlet 32 toward the outlet 36, forexample, from some external pressurizing device like a pump, or from apath open to the pressure surface 26 and communicated directly to thebleed path 30, or the like.

As shown in FIG. 1, the inlet 32 may be of any suitable size and shape.For example, the inlet 32 may be a slot that may extend in a generallyradial direction over at least a portion of an area of the suctionsurface 28 that would experience boundary layer separation but for theslot. However, the inlet 32 may be disposed at any suitable angle withrespect to the axis B, and need not be centered between the leading andtrailing surfaces 22, 24. In another example, the inlet 32 may be aporous patch on the suction surface 28. For instance, the conduit 34 orat least a portion thereof may be covered by a porous surface flush withthe suction surface 28. An example porosity of the porous patch may be10%-75% porosity.

Prior art FIG. 5 illustrates a prior art blade 114 without the bleedpath 30, wherein laminar separation and turbulent reattachment occursover a suction surface 128 to create a bubble area 129 of low energyworking fluid. Such a bubble area 129 tends to appear at low Reynoldsnumbers, creates drag and thereby reduces efficiency of the blade 114and, in a propeller embodiment, requires more power to move the blade114.

FIG. 6 illustrates another exemplary embodiment of a rotor blade 214.This embodiment is similar in many respects to the embodiment of FIGS.1-4 and like numerals between the embodiments generally designate likeor corresponding elements throughout the several views of the drawingfigures. Additionally, the descriptions of the embodiments areincorporated by reference into one another and the common subject mattergenerally may not be repeated here. In contrast to prior art FIG. 5,FIG. 6 illustrates a presently disclosed rotor blade 214 having an inlet232 of a bleed path 230 disposed in area of the suction surface 228where the bubble area 129 (FIG. 5) would be located if the bleed path230 were not present. In this embodiment, the inlet 232 can be providedas a porous surface or patch to cover the bubble area 129 (FIG. 5). Theinlet 232 may be centered (in a circumferential direction between) overan area where the bubble area 129 (FIG. 5) would be. Those of ordinaryskill in the art will recognize that such sizing and locating isapplication specific and may be determined via empirical testing or bymodeling or both.

In a further embodiment, shown in FIG. 4, a plurality of the inlet 32may be provided, each of which may be sized in correspondence to aradial fluid flow distribution. For example, the inlet 32 may be dividedin a radial direction into a plurality of separate inlets, as indicatedin FIG. 4, corresponding in size and/or shape to different radialpressure gradients along the blade 14. Such an inlet 32 may be thoughtof as akin to an input side of a harmonica.

Referring to FIGS. 1-4, the conduit 34 may include any suitable deviceto convey the working fluid. In one embodiment, the conduit 34 mayinclude one or more separate tubes, pipes, hoses, or the like assembledto the blade 14 in any suitable manner. In another embodiment, theconduit 14 may include an integral void in the blade 14 that may beformed, cast, forged, machined, or the like in the blade 14 in anysuitable manner. The conduit 34 may be of any suitable shape and size.

As shown in FIG. 3, the outlet 36 may be located in the trailing surface24 of the blade 14 in one embodiment. In another embodiment, an outlet36′ may be provided in the suction surface 28. In an additionalembodiment, both outlets 36, 36′ may be used. In any case, the outlet 36(and/or 36′) may be located radially inwardly of the radially outermostsurface 20 of the blade 14. The outlet 36 or outlets 36, 36′ may be ofany suitable shape(s) and size(s).

In one embodiment, the conduit 14 and/or the outlet(s) 36 (36′) may beshaped and/or sized to reduce a differential between a velocity ofworking fluid transmitted from the outlet 36 and a velocity of workingfluid in a free stream adjacent the outlet 36. Those of ordinary skillin the art will recognize that such shaping and sizing is applicationspecific and may be determined via empirical testing or by modeling orboth.

The presently disclosed bleed path 30 reduces, eliminates, or preventsboundary layer separation over the suction surface 28 of the rotor blade14, with concomitant reduction, elimination, or prevention in drag andinefficiency of the blade 14. For example, the bleed path 30 may be usedto reduce, eliminate, or prevent boundary layer separation whether theflow is laminar or turbulent, and may be particularly beneficial for usein applications with low Reynolds numbers. For instance, it is believedthat the presently disclosed bleed path 30 will reduce power required torotate a propeller and may increase propeller efficiency particularlyfor relatively small, slowly rotating propellers at high altitudes.Moreover, the bleed path 30 reduces product weight, is low in cost, anddoes not have any separate moving parts.

Generally, airfoils are designed such that the boundary layertransitions from laminar to turbulent prior to laminar separation. Theturbulent boundary layer then naturally remains attached longer becauseit can tolerate a more adverse pressure gradient than that of a laminarboundary layer. However, at low Reynolds numbers, the laminar boundarylayer may separate before transition occurs. If the laminar flowseparates, then the process of separation usually induces rapidtransition to turbulence. In many cases, this turbulent flow thenreattaches because it is more tolerant of the adverse pressure gradientwhich caused the laminar flow to separate. This laminar separation andturbulent reattachment is called a laminar separation bubble and is acommon source of high drag on airfoils used at low Reynolds numbers. Inother cases, the separated flow does not reattach, and the resultingdrag is even higher.

The presently disclosed passive bleed path(s) may improve efficiencyover a large range of conditions, especially at low Reynolds numberswhere laminar separation tends to appear. The bleed inlet(s) may belocated near the region where laminar separation would occur (if bleedwere absent). At low Reynolds numbers, the passive bleed preventslaminar separation such that the boundary layer transitions to turbulentwhile still attached. The turbulent boundary layer is then able toremain attached because it is more tolerant of an adverse pressuregradient. Therefore, a laminar separation bubble can be prevented, and asubstantial source of drag can be eliminated.

Although the bleed inlet(s) may be located near the region of laminarseparation, the passive bleed may also be beneficial at higher Reynoldsnumbers, when the flow is already turbulent over the bleed inlet(s). Inthis case, the natural turbulent separation point is downstream of thelocation of the bleed inlet(s), even if bleed were absent. With passivebleed present, the turbulent boundary layer is thinned, thereby delayingseparation to a point even farther downstream. This could allow moreextreme airfoil shapes to be practical.

This description, rather than describing limitations of an invention,only illustrates example embodiments of the invention recited in theclaims. The language of this description is therefore exclusivelydescriptive and non-limiting. Obviously, it's possible to modify thisinvention from what the description teaches. Within the scope of theclaims, one may practice the invention other than as described above.

1. A rotor blade comprising: a root region; a tip region disposedradially outwardly of the root region; a leading surface extendingbetween the root and tip regions; a trailing surface extending betweenthe root and tip regions; a pressure surface extending between the rootand tip regions and the leading and trailing surfaces; a suction surfaceextending between the root and tip regions and the leading and trailingsurfaces; and a bleed path opening to the suction surface, extendingthrough the blade, exiting to at least one of the suction or trailingsurfaces, and through which working fluid flows under centrifugalpumping forces when the blade rotates, to passively bleed working fluidfrom the suction surface.
 2. The rotor blade of claim 1, wherein theworking fluid passively flows through the bleed path under negativepressurization, but the working fluid does not actively flow through thebleed path by positive pressurization from some external pressurizingdevice or from a path open to the pressure surface.
 3. The rotor bladeof claim 1, wherein the bleed path includes: an inlet in the suctionsurface to receive working fluid on the suction surface; a conduit incommunication with the inlet to convey the working fluid from the inlettoward the tip region; and an outlet in communication with the conduitand disposed radially outwardly of the inlet to exhaust the workingfluid out of the blade.
 4. The rotor blade of claim 3, wherein the bleedpath is configured to cause centrifugal pumping forces to pull theworking fluid into the inlet, through the conduit, and out of the outletwhen the blade rotates.
 5. The rotor blade of claim 3, wherein the bleedpath is located radially outward of a circumferential axis bisecting theblade.
 6. The rotor blade of claim 3, wherein the inlet is a slotextending in a generally radial direction along the blade.
 7. The rotorblade of claim 3, further comprising a plurality of the inlet radiallyspaced from one another in correspondence to radial pressure gradients.8. The rotor blade of claim 3, wherein the conduit is at least one ofshaped or sized to reduce a differential in velocity of working fluidtransmitted from the outlet and velocity of working fluid in a freestream adjacent the outlet.
 9. The rotor blade of claim 3, wherein theoutlet is located in at least one of the suction surface or the trailingsurface.
 10. The rotor blade of claim 3, wherein the outlet is locatedradially inward of a radially outermost tip of the blade.
 11. The rotorblade of claim 1, wherein the rotor blade is a working member of atleast one of an aircraft propeller, a marine propeller, a helicopterrotor, a turbine engine rotor, or a windmill impeller.
 12. A rotorcomprising: a hub defining a rotational axis of the rotor; and a rotorblade extending radially outwardly from the hub, and including: a rootregion; a tip region disposed radially outwardly of the root region; aleading surface extending between the root and tip regions; a trailingsurface extending between the root and tip regions; a pressure surfaceextending between the root and tip regions and the leading and trailingsurfaces; a suction surface extending between the root and tip regionsand the leading and trailing surfaces; and a bleed path opening to thesuction surface and including: an inlet in the suction surface toreceive working fluid on the suction surface; a conduit in communicationwith the inlet to convey the working fluid from the inlet toward the tipregion; and an outlet in communication with the conduit and disposedradially outwardly of the inlet to exhaust the working fluid out of theblade; wherein the bleed path is configured such that working fluidflows through the bleed path under centrifugal pumping forces when theblade rotates, to passively bleed working fluid from the suctionsurface, such that the working fluid passively flows through the bleedpath under negative pressurization, but the working fluid does notactively flow through the bleed path by positive pressurization pushedfrom the inlet toward the outlet from some external pressurizing deviceor from a path open to the pressure surface.
 13. The rotor of claim 12,wherein the bleed path is located radially outward of a circumferentialaxis bisecting the blade, and the inlet is a slot extending in agenerally radial direction along the blade.
 14. The rotor of claim 12,wherein the outlet is located in at least one of the suction surface orthe trailing surface, and is located radially inward of a radiallyoutermost tip of the blade.
 15. The rotor of claim 12, wherein the rotoris at least one of an aircraft propeller, a marine propeller, ahelicopter rotor, a turbine engine rotor, or a windmill impeller.
 16. Arotor blade comprising: a root region; a tip region disposed radiallyoutwardly of the root region; a leading surface extending between theroot and tip regions; a trailing surface extending between the root andtip regions; a pressure surface extending between the root and tipregions and the leading and trailing surfaces; a suction surfaceextending between the root and tip regions and the leading and trailingsurfaces; and a bleed path opening to the suction surface and including:an inlet in the suction surface to receive working fluid on the suctionsurface; a conduit in communication with the inlet to convey the workingfluid from the inlet toward the tip region; and an outlet incommunication with the conduit and disposed radially outwardly of theinlet to exhaust the working fluid out of the blade.
 17. The rotor bladeof claim 16, wherein the bleed path is configured such that workingfluid flows through the bleed path under centrifugal pumping forces whenthe blade rotates, to passively bleed working fluid from the suctionsurface, and such that the working fluid passively flows through thebleed path under negative pressurization, but the working fluid does notactively flow through the bleed path by positive pressurization fromsome external pressurizing device or from a path open to the pressuresurface.
 18. The rotor blade of claim 16, wherein the bleed path islocated radially outward of a circumferential axis bisecting the blade,and the inlet is a slot extending in a generally radial direction alongthe blade.
 19. The rotor blade of claim 16, wherein the outlet islocated in at least one of the suction surface or the trailing surface,and is located radially inward of a radially outermost tip of the blade.20. The rotor blade of claim 16, wherein the rotor blade is a workingmember of at least one of an aircraft propeller, a marine propeller, ahelicopter rotor, a turbine engine rotor, or a windmill impeller.